Method for making a gas transfer device



1968 A. DouNoucos METHOD FOR MAKING A GAS TRANSFER DEVICE 2 Sheets-Sheet1 Filed June 30, 1967 [r7 vent 02". A r g e/o Dounoucos, am Maw HA5 A :5b onvey 17, 1963 A. DOUNOUCOS METHOD FOR MAKING A GAS TRANSFER DEVICE 2Sheets-Sheet 2 Filed June 30, 1967 inventor.- A)? e/o .Doanoucas,

may a At; borne United States Patent 3,416,985 METHOD FOR MAKING A GASTRANSFER DEVICE Angelo Dounoucos, Schenectady, N.Y., assignor to GeneralElectric Company, a corporation of New York Continuation-impart ofapplication Ser. No. 482,770, Aug. 26, 1965. This application June 30,1967, Ser. No. 650,465

6 Claims. (Cl. 156--289) ABSTRACT OF THE DISCLOSURE A soluble coating isput into a wire screen at a location on the edge where it is desired tohave a flow passage. The wire screen is then disposed betweenpermselectivc membranes contiguous therewith so that after the sandwicharrangement of screen and membranes is bonded at its edges to form asealed composite layered exchanger, the coating can be washed out toleave a passage through the scaled edges into the woven screen.

This application is a continuation-in-part of my copending applicationSer. No. 482,770, filed Aug. 26, 1965, and assigned to the same assigneeas the present application. My present invention relates to a gasexchanger and an improved method for making such a gas exchanger forselectively transferring gas from one area to another.

As pointed out in the application referred to above, many applicationsand modern technology require the selective extraction of one gas from agroup ofgases and the transfer of that gas to another fluid medium. Therelationship between the gas and the medium to which it is beingtransferred should be such that an optimum or nearly optimum exchangerrelationship exists for transfer of gas. A preferred arrangement is onewhere the gas to be transferred and the receptive medium flow in nearlyopposite directions across the membrane faces. A compact gas exchangeapparatus is needed for transferring a selected gas to a receptive fluidmedium. An exchange apparatus is arranged and sealed to prevent unwantedgasses from interfering with the exchange process and provide the mosteffective transfer of gas into the medium. This is done by using thecounterflow principle.

One problem encountered in making a plurality of stacked chambers havingmembranes therebetween and alternately containing gas and receptivefluid medium is that when these elements of the gas exchanger areassembled and sealed together, the sealing compound runs into the holethrough which the fluids involved are to be passed and blocks the holeto the point that the fluids are ob structed. One solution described inthe aforementioned copending application has been to put preformed plugsin these areas cutting away the wire so that the plugs can be fittedinto the cutaway space. These plugs do not always fit perfectly into thecutaway space and then the woven mesh between the membranes is cutleaving jagged edges which may break or cut the membranes andthe plugsmay adhere somewhat to the sealingcompound making them diflicult toremove without breaking or otherwiseharming the sealing compound.

It is a principal object of my invention to provide an improved gastransfer apparatus which efficiently transfers a fluid from one mediumto a receiving medium.

It is an object of my invention to provide improved means for leavingflow conducting holes through the seallng compound between porousmembranes.

It is another object of my invention to provide an improved method andmeans for leavingflow conducting holes which may be easily applied inthe manufacture of gas exchangers.

3,416,985 Patented Dec. 17, 1968 "ice In brief, my invention involvesthe formation in situ of a soluble material, such as a water soluble waxpluglike spacer embedding the woven wire membrane spacer where it isdesired later to have an opening, sealing stacked alternate wire spacerand permeable membranes together by means of a sealing compound aroundthe edges of the stack and then washing away the soluble materialleaving holes in the sealing compound through which the desired fluidmediums may enter and be circulated in the space between adjacentmembranes.

In carrying out the objects of my invention, I provide a highlyefficient gas exchange apparatus being a flat planar imperforatemembrane barrier, selectively permeable to certain gases, which isplaced in a chamber or between chambers through which one of thoseselected gases flows and a chamber in which flows a fluid that isreceptive to the selected gas. A vulcanizing potting compound isemployed to seal the edges of the apparatus save for entrance and exitopenings, so that unwanted gases or other fluids are prevented fromentering into either chamber and interfering with the gas transferringprocess taking place. In the preferred embodiment of this invention thecorners of the apparatus are dipped into a polyethylene glycol materialbefore the potting compound is applied. In this way, the polyethyleneglycol material can be washed away later leaving access openings at eachcomer of the gas exchanger to the passage of fluids through theapparatus. A header can be placed over each corner so that fluid may bepassed to and from the exchanger on a selected basis. Preferably thedirection of flow of the gas in one chamber is at apposite or more orless right angles to the direction of flow of the receiving fluid.through the other chamber so that an optimum amount of gas may betransferred through the semipermeable membrane to the receiving fluid.Also, a plurality of stacked chambers having membranes therebetween andalternately containing gas and receptive fluid medium are employed forincreasing the efficiency and capacity of the gas transfer apparatus.

The attached drawings show preferred embodiments of my invention inwhich:

FIGURE 1 is a view of the gas transfer device of my invention.

FIGURE 2 is an enlarged sectional view of the apparatus of FIGURE 1before the sealing compound has been applied.

FIGURE 3 is an enlarged sectional view of the apparatus of FIGURE 1after the sealing compound has been applied.

FIGURE 4 shows a stacking arrangement of the membraned package.

FIGURE 5 shows the sealed membrane package and illustrates thecounterflow configuration through this package.

' FIGURE 6 shows an enlarged view of a corner of FIGURE 5 with the waxymaterial washed away.

, In the-view of the gas transfer apparatus shown in FIGURE}, a suitableimperforate' membrane 2 which is selectively permeable to certain gases,forms a separation means between chambers} and (through which thefeed-gas to[be transferred and the receiving medium,

respectively,flow. Particularly valuable as 'a'mixture for use as a feedgas is oxygen or air. Membrane 2'is constructed of an imperforatematerial, such as the silicone rubber membranes of patent applicationsSer. Nos. 241,- 346, filed Nov. 30, 1962 (now US. Patent 3,256,675);247,904, filed Dec. 28, 1962 (now U.S. Patent 3,274,750); 269,430, flledApr. 1, 1963 (now abandoned); 397,687, flled Sept. 21, 1964 (now U.S.Patent 3,350,687), and 466,698, tiled June 6, 1965 (now US. Patent3,325,330), by Walter L. Robb and assigned to the assignee of thepresent invention, which permit certain specific gases or vapors to passtherethrough to the substantial exclusion of others. The gases or vaporsthat permeate the membrane pass from the side of greater partialpressure to the side of lesser partial pressure.

For example, if the partial pressure of oxygen gas flowing throughchamber 3 is 3.1 lbs/sq. inch, this would be in the case of oxygen inair, and the partial pressure of oxygen and the medium flowing throughchamber 4 is far less, oxygen gas will readily permeate membrane 2 tomix with the second fluid medium. Thus, the fluid passing throughchamber 4 will be enriched at the expense of the richer concentration ofoxygen in chamber 3.

FIGURES 2 and 3 display the invention disclosed in the aforementionedcopending application, Ser. No. 482,770, now US. Patent 3,354,618,except that soluble plugs are employed. The membranes 2 are stacked in asurface-tosurface parallel array with the screens 5 or other reinforcingmeans interlenved therebetween. The screens allow the passage of fluidin a longitudinal direction and cause turbulence and mixing. The screensallow the fluid to pass without rupturing the membrane since themembrane is supported at many points by the screens. Support provided byscreens 5 can be sufficiently great so that large absolute pressuredifferentials can exist across the membrane, if this is desired. Thescreens may be fabricated of a suitable plastic or metal made in theconventional cross-hatched woven fashion.

The stack of membranes and screening is prepared for being securedtogether by interspersing the cutout edges 6, 7 of each screen withspacers 8, as shown in FIGURE 2, later withdrawal of which forms theports or gaps 9 in the securing compound. These ports 9 are tii'entranceand exit openings through which gases and other fiuids pass into the gasexchange apparatus. Spacers 8 are made of a material such aspolytetrafluoroethylene that does not adhere to the sealing compound.Thus, when a planar configuration is employed with a plurality ofmembranes 2 as shown in FIGURES l and 2, spacers 8 are preferably flatand of a height equal to the desired space between the membranes 2 sothat the spacers 8 not only form the entrance and exit channels, butalso support the membranes in a desired relationship to each other whilethey are being secured together. While a rectangular membrane and spaceris shown in the illustrative figures it will be appreciated that theseshapes are only one of the numerous shapes that can be employedsuccessfully with my invention. By properly positioning spacers 8 thetransfer gas flows through chamber 3 in a direction opposite to thedirection that the receiving medium flows through chambers 4, so that acounterflow relationship"betweemthe gas and receiving mediuiii is"achieved.

When the membranes, screens and spacers are properly arranged in packageform as shown in FIGURE 2, the edge of the package may be dipped in asuitable sealing compound 10, preferably a vulcanizing rubber compoundsuch as the curable siloxane potting compounds described in US. PatentNo. 3,133,891 to Louis Cezzeriat. This compound may be painted on solong as a firm seal is maintained. It the stacked membranes, screens andspacers are inserted into the potting compound, each edge of theapparatus should be inserted in the potting compound to a depth shown bythe guidelines 11, i.e., sufficient to effectively secure the membranestogether and form a secure leak-proof seal that prevents any extraneousgases from entering the apparatus and interfering with the transferprocess taking place. Outside gas would disturb the partial pressurelevels being maintained and also the flow relationship taking placewithin the device. As shown in FIGURE 2, spacers 8 extend beyond theline ll so that the channels formed by these spacers extend completelythrough the potting compound and the entrance and exit channels formedare not affected by the sealing substance. The curable siloxanementioned above sets quickly and without the application of any pressureto the apparatus. With the present sealing procedure intricate channelsmay readily be produced, to form the desired counterflow gas exchangeapparatus, as previously described.

it is readily seen in FIGURE 1 that gas to be transferred enters theapparatus through one of the sets of ports formed by cutouts 7 forexample, and diffuses throughout the adjacent chamber 3 to occupy theentire volume and cover the membrane area. In like manner, the gasreceiving medium enters chamber 4 through entrance means or port tosubstantially fill the chamber and cover the other surface area of themembrane. The gas having the higher partial pressure now passes throughthe membrane in the direction of the fluid medium having the lowerpartial pressure.

A theoretical discussion of the operation of FlGURE l is to be found inmy copending application referred to above and will be omitted here.

While the discussion above is directed to one membrane and supportingstructure, it may be appreciated that a series of laminations are builtup and that the transfer of gas will be faster and more uniform becauseof the greater amount of gas in proximity to the membranes because ofreceiving media on the other side. It is noted that any of the apparatusI have described may be constructed in the single or multiple stackedarrangement as described with respect to FIGURE l.

FIGURES 4, S, and 6 display the improved construction of the instantinvention. The top element of the gas exchanger is a woven screen 12having diagonally opposed corners coated with a thin layer of specialwax 13 and the opposing comers removed as shown. The next element downfrom the top is a permselective membrane 14 which is adapted for thespecial purpose of selectively allowing diffusion of a particular gasthrough it. Each membrane element has all four corners removed. Thethird element is another woven screen 15 having different comers fromthe top element 12 coated with a thin layer of special wax and its othercomers removed. The fourth element is another permselective membrane 16similar in character to the second element and the fifth element is awoven screen 17 having different diagonal corners coated with a thinlayer of wax the same as the first element. In this way, a stackingarrangement of many layers may be made and every alternate woven screenwill have a wax coating over the same corners to allow flow through thegas exchanger. These elements are held together in a firm manner and theouter edge is coated with a sealing compound. Sealing may beaccomplished by casting a narrow seal around the entire peripherybetween each layer of membrane with the exception of the four corners.Each woven screen separator has been coated on two opposite corners witha low temperature melting waxy material 13 which solidifies at roomtemperature and is very soluble in water so that it may be washed awayby the application of water. The wax should be selected to have as low amelting point as possible but the melting point should be above anytemperature to which it would be subjected in the process. An example ofsuch waxes are the commercially available polyethylene gylcols with anaverage molecular weight between about 700-20,000 grams. These waxes arehighly soluble in water to allow later removal by washing. Thus, thefinal product will be a stack of alternate layers of permselectivemembrane and wax coated screen with alternate layers of screen havingthe wax filled corners reversed as shown in FIGURE 5. Of the fourcorners, only two opposed ones are coated with the temporary coveringmaterial while the remaining corners are fully closed by sealingcompound. These comers having been precut,are fully embedded in thesealing compound. This prevents leakage from within the exchanger. inorder to seal these elements together, the assembly of a desired numberof membranes and screens may be placed in a mold which is open along thefour peripheral edges and the entire assembly is then cast in sealingcompound so that each peripheral edge in sequence has sealing compoundat ambient temperature to a depth depending on the size of the unit andthe internal pressure which is expected to be applied. As readily seen,sealing cornpound will enter all peripheral edges where the wax is notpresent and will bond the woven screen to the permselective membranearound the edges since a thin sealant coating will finally completelycover the assembly. A sawcut is then made at each corner (as shown inFIGURE 5) to remove the sealing compound and expose the wax. The exposedscreen edges contain wax at each comer. The removal of this wax isaccomplished by fiushing each corner with some suitable solvent such aswarm water. When the wax is removed, the area of each screen which wasformerly filled with wax now forms conduits 17, 18 and 19, 20 open tothe flow of the fluids which are to be exchanged. Shapes other thanrectangular can be employed within the spirit of this invention andcover plates are mounted above the top screen and below the bottomscreen. For example, if a hexagonal shape is employed three fluidstreams may be passed through the apparatus and the use of a round gasexchanger would simplify the sealing step since the round gas exchangerhas a continuous edge which simplifies the sealing step that may be doneby centrifuging or by rotating the edge of the round gas exchangerthrough a bath of sealing compound.

The configuration shown in FIGURE 5 allows flow which closely approachescounterfiow relationship as shown by the how lines. In this embodiment,if a carbon dioxide laden gas is supplied at one corner and exited atthe other comer, then a scrub gas can be fed at a third 3 corner andwill flow in a more or less opposite direction from the feed gas thusextracting from the feed gas through the membranes, a large percentageof the carbon dioxide. The enriched scrub gas will then pass out of thegas exchanger at the fourth corner.

The blown up view (FIGURE 6) of the corner of FIGURE 5 shows the resultwhen the sealing compound has penetrated some distance into the wovenscreen and lies between permselective membranes above and below thisscreen. When the wax is removed the exchange fluid can be passed in andout of the first and third layers shown here while the second and fourthwoven wire layer will not admit passage since it has been blocked off bythe sealing compound.

Some of the advantages of this improved method of forming are asfollows. It is not necessary to cut the screen. This simplifies themanufacturing process and avoids weakening the screen. The sharp edgesand burrs left after cutting will all be on the outside periphery ratherthan located internally where they might pierce 6 The foregoing is adescription of an illustrative embodiment of the invention, and it isapplicant's intention in the appended claims to cover all forms whichfall within the scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A method for making a gas transfer device comprising the steps of thesemipermeable membranes causing leakage betweenthe streams. The removalof the plug-like wax spacers formed in situ is facilitated since thewaxy plugs are removed by dissolution. Possible splitting and chippingof the sealing compound is avoided by washing the plug out. Finally,when the sealing compound is applied to the precut woven screen and theprecut membrane the compound covers the cuts and a leak-free seal isassured.

applying to opposed edge sections of woven screen separators a liquidmaterial which solidifies at room temperature and may be removed bydissolution, permitting said material to solidify, placing a pluralityof imperforate membranes in parallel surface-to-surface stacked arraywith woven screen separators therebetween so that first and second fiowareas are formed alternately,

applying a siloxane potting compound to the edges of the membranes toseal and to enclose the first and second fiow areas and effectivelyseparate them from each other so that fluid flowing in a flow area mustpermeate a membrane to reach another flow area, and

dissolving away said material from said opposed edge sections so thatpassages are formed to permit flow to be directed in substantiallyopposite directions through the first and second flow areas forproviding a partial pressure difierential across the membrane thatresults in optimum gas transfer relationship.

2. A method for making a gas transfer device as set forth in claim 3 inwhich the material is an ethylene polyglycol derivative.

3. A method for making a gas transfer device as set forth in claim 2 inwhich said ethylene polyglycol material has an average molecular weightbetween about 700-20,000 grams.

4. A method for making a gas transfer device as set forth in claim 1 thestep of cutting off the corners of said sealed stacked array afterapplying said siioxane potting compound and before dissolving saidmaterial sway.

5. A method for makings gas transfer device as set forth in claim 3 inwhich said siloxane potting compound is at room temperature.

6. In a method 'for making a gas transfer device as set forth in claim 3the step of removing edge sections remote from said opposed coated edgesections before applying said material so that said sealing materialwill cover said edge sections.

References Cited UNITED STATES PATENTS 1,983,939 12/1934 Kehr 156-305 X2,608,502 8/1952 Merriman 156-289 X 3,033,734 5/1962 Price l56-305HAROLD ANSHER, Primary Examiner.

US. Cl. X.R.

